In 1999, the research of database systems' execution time breakdown on modern computer platforms has been analyzed by Ailamaki, et al. The primary motivation of these studies is to improve the performance of Disk Resident Databases (DRDBs), which form the main stream of database systems until now. The typical benchmark used in those studies is TPC-C. However, continuing hardware advancements have "moved-up" on the memory hierarchy, such as the larger and larger on-chip and off-chip caches, the steadily increasing RAM space, and the commercial availability of huge flash memory (solid-state disk) on top of regular disk, etc. To reflect such a trend, the target of workload characterization research along the memory hierarchy is also studied. This paper focuses on Main Memory Databases (MMDBs), and the TPC-H benchmark. Unlike the performance of DRDB which is I/O bound and may be optimized by high-level mechanisms such as indexing, the performance of MMDB is basically CPU and memory bound. In this study, the paper first compares the execution time breakdown of DRDB and MMDB, and the paper proposes an optimize strategy to optimize the memory resident aggregate. Then, the paper explores the difference between column-oriented and row-oriented storage models in CPU and cache utilization. Furthermore, the paper measures performance of MMDBs on different generational CPUs. In addition, the paper analyzes the index influence and gives a strategy for main memory database index optimization. Finally, the paper analyzes each query in the full TPC-H benchmark in detail, and obtains systematic results, which help design micro-benchmarks for further analysis of CPU cache stall. Results of this study are expected to benefit the performance optimization of MMDBs, and the architecture design memory-oriented databases of the next generation.